This invention relates generally to inflatable passive restraint systems such as used in motor vehicles to restrain the movement of a seated occupant during a collision. One aspect of the invention is more particularly directed to an improvement in the design of an air bag module used in such restraint systems to minimize deformation of the module and possible damage to the dashboard and/or instrument panel of a vehicle with the deployment of the air bag. Such improvement is in the structure internal to the module for a) housing and positioning the inflator and the air bag and b) directing the inflating gas flow or jet for best deployment of the air bag.
In another aspect, the invention more particularly relates to an improvement in the structure used in such systems for housing a gas generation material and an inflatable bag to further reduce the weight of the assembly and to permit the more effective and economical incorporation therein of various design features.
Some terminology herein is used for convenience in reference only and is not intended to be limiting. The words "forwardly" and "rearwardly" refer to the normal forward and reverse directions of travel of the vehicle to which a passenger passive restraint module is attached. The phrase "thrust neutral" refers to the production by an inflator of zero thrust when initiated as, for example, during a deployment event or accidentally such as during shipping, storage, or handling thereof. That is to say, the gas discharge openings in the inflator are so positioned that the gas is discharged in opposing directions whereby there are no resulting forces tending to cause physical movement of the inflator. Hence, the inflator will expend the energy generated thereby, generally in place.
The state of the prior art is indicated by the following U.S. patents:
______________________________________ U.S. Pat. No. Issue Date Patentee ______________________________________ 3,414,292 December 3, 1968 S. Oldberg et al. 3,715,131 February 6, 1973 E. K. Hurley et al. 3,880,447 April 29, 1975 W. F. Thorn et al. 4,332,398 June 1, 1982 G. R. Smith 4,817,828 April 4, 1989 G. W. Goetz 4,832,300 June 27, 1989 J. F. Ziomek et al. 4,941,678 July 17, 1990 D. R. Lauritzen et al. ______________________________________
The Oldberg et al. patent discloses a safety device for providing protection for vehicle passengers comprising a folded inflatable crash bag closely surrounding an elongated cylindrical diffuser member, being secured thereto by clamps. The diffuser member defines a chamber in which an inflator comprising a fluid reservoir in an inner container is concentrically located. For providing a tight seal the inner container is seam welded at the opposite ends thereof to the diffuser member. When activated by explosive means, fluid from the reservoir flows rearwardly from one side only of the inflator against an adjacent inner wall of the diffuser member. The flow divides and is discharged forwardly through a single row of longitudinally spaced apart openings, that are provided on one side only of the diffuser member, against a fixed baffle member. The baffle member divides and redirects the fluid rearwardly into the inflatable bag.
In the fabrication and assembly of inflatable devices for protecting vehicle passengers, the inflator poses a large potential hazard. Accidental initiation thereof during shipping, storing and installation in the safety device could result in injury to personnel and also cause property damage, particularly when the inflator is not of the thrust neutral type. Thus, in order to minimize the possibility of such injury and damage, it is desirable to reduce the amount of handling to which the inflator is subjected during the fabrication and assembly of the safety device. Installation of the inflator as a last operation in the assembly of the device would provide a substantial reduction in the risk of injury and damage. With the use of an inflator of the thrust neutral type, the risk of such injury and damage would be further reduced.
The construction of the Oldberg et al. safety device is such as to preclude installation of the inflator as a last operation of the assembly of the device. Specifically, the inflatable bag is provided in closely surrounding relation to the diffuser member, with the inflator, that is, the inner container, welded at the ends thereof to the diffuser member. Moreover, with fluid flowing from the reservoir of fluid from one side only of the inflator and from one side only of the diffuser member, neither the inflator alone, nor the inflator and diffuser member, as a unit, are thrust neutral.
The Hurley et al. patent discloses a folded inflatable bag surrounding a gas generator having a head assembly of cylindrical shape provided with a closed end and an open aft end that is closed by a closure plate. A centrally positioned orifice that is normally closed by a rupture disc is provided in the closure plate. Enclosing the cylindrical portion of the head assembly is a concentrically positioned diffuser having a closed end in the shape of a dished head, thereby providing an annular cavity about the gas releases, in response to pressure in the head assembly exceeding the burst pressure of the disc, thereby allowing the generated gas to flow out of the orifice in the closure plate of the aft end of the gas generator and to impinge on the inner wall at the end of the diffuser. This causes the gas to be dispersed into the annular cavity and out of a plurality of openings spaced around the wall of the diffuser. With the generated gas flowing out of the aft end of the gas generator, the operation thereof is not thrust neutral. Nor does the Hurley construction allow fabrication of the device with the installation of the gas generator as a last operation of the assembly.
The Thorn et al. patent discloses a folded inflatable bag positioned in close contact with an elongated cylindrical gas generator. The gas generator is provided with rows of gas outlet ports that extend 360.degree. around the cylinder. The gas is discharged in opposing directions and produces counteracting thrusts, and thus, is thrust neutral. A gas redirecting plate in the shape of a half cylindrical container is positioned in spaced relation around the forwardly facing portion of the gas generator. The plate redirects forwardly discharged inflating gas in a rearward direction into the inflatable bag. Redirected gas together with gas that directly is discharged into the inflatable bag deploy the bag, which normally is folded, to an inflated condition. In the stored position thereof, the bag is positioned closely adjacent to and in contact with the rearward half side of the gas generator. This precludes installation of the gas generator as a last operation in the assembly of the apparatus.
The Smith patent discloses an inflatable restraint system including a folded inflatable cushion, a concentric elongated cylinder inflator-diffuser combination, and an elongated horizontally orientated nozzle. The inflator and diffuser are located within the confines of the folded cushion and are connected as a unit to the side walls of a housing therefor by means of bolts which extend into tapped bosses, which bosses are rigid with the combined unit. Consequently, neither the combined unit, nor the inflator can be installed as a last operation in the assembly of the system.
In the Goetz patent an elongated cylindrical inflator and a folded air bag are mounted in a rigid reaction canister which is fixed to the dashboard of a vehicle, with the orientation and arrangement of gas discharge openings or exhaust ports in the inflator being such that, when activated, an initial flow generated gas is directed rearwardly by the inflator to inflate the bag. Excess gas flows from the inflator in a forward direction into the surrounding environment. This result is achieved by using rupturable foil layers to close both forwardly and rearwardly directed inflator exhaust ports, with rupturing of the rearwardly directed ports occurring at a pre-selected pressure that is lower than the pressure at which the forwardly directed ports rupture. Thus, the inflator is not thrust neutral, nor is it capable of installation as a last operation of the assembly of the apparatus because of the positioning in the reaction canister of the folded air bag in close proximity to the inflator.
As disclosed in the Goetz patent and the other aforementioned prior art patents, it is known in prior art installations to provide a container to house the air bag and the inflator. The container is generally referred to as a reaction canister and provides a medium for installing and retaining a module in the instrument panel by the utilization of suitable brackets.
The reaction canister provides protection for the inflator, the diffuser, if provided, and the air bag until the time of deployment of the bag. Additionally, the reaction canister absorbs the loads that are produced upon deployment of the bag, which loads, typically, are large. Unless sufficiently absorbed, such loads can cause serious damage to the interior of the vehicle, and in particular, to the instrument panel.
A drawback to the use of a reaction canister in an air bag module for passenger protection is the envelope in the dashboard or instrument panel that is allotted for the installation of the module. Resulting restrictions, usually in height, causes lengthened, that is, deeper, top and bottom panels in order to accommodate the folded volume of the air bag. The bag is then restricted for unfolding and must travel rearwardly a distance greater than desirable before unfolding. Because of the large amount of gas that is produced and the distance the bag needs to travel before unfolding, pressure builds up in the reaction canister to a level that tends to expand the canister and cause it to bulge. This condition, known as bell mouthing, is very destructive of the instrument panel, and is particularly objectionable in low speed crashes where other damage to the vehicle is small.
The Ziomek et al. patent and the Lauritzen et al. patent disclose the use of a tether strap to resist the spreading forces on the reaction canister and thereby preclude bell mouthing upon deployment of the air bag. This technique allows the use of lighter weight and less expensive reaction canisters. The structural arrangement, however, leaves something to be desired in respect of the introduction of undesirable complication into the manufacturing and assembling operations, and moreover, does not allow installation of the inflator as a last operation in the assembly of the module.
Thus, in general, air bag module assemblies of the prior art generally include three basic components: 1) a cushion or air bag that is inflated with gas such as when the vehicle encounters a sudden deceleration, 2) an inflator which upon actuation serves to provide the gas used to inflate the air bag, and 3) a reaction canister which typically functions as a structural housing supporting both the inflator and the air bag while providing a mounting base for installation of the assembly in a vehicle and direction to the resulting from the inflator.
In general, because of the relatively high pressures generated in conventional inflators, e.g., pyrotechnic inflators commonly produce pressures in the range of about 1500-3000 psi, the walls of such inflators are typically fabricated of relatively thick material to provide additional strength thereto. However, as described above, in conventional air bag module assemblies, the inflator is typically housed within a walled reaction canister. The use of such thick walled inflators housed within a walled reaction housing typically results in an assembly of greater weight than is optimally desired.
Further, as reaction canisters are commonly fabricated using formed and/or welded steel, such fabrication techniques are not conducive to the economical and effective incorporation therein of various desired features, such as various mounting or attachment preparations, for example, in particular vehicular inflatable restraint system design applications.
Still further, an increasing emphasis on weight reduction in automobiles has created a need and a demand for a lighter weight inflatable restraint system.
Thus, there is a need and a demand for an improved reaction canister for use in an air bag module for the passenger side of a vehicle.